LM393DR - Dual Differential Comparator from Texas Instruments

What Is LM393DR and How Does It Work?

A comparator compares two analog voltages and outputs a digital signal indicating which is higher. When the non-inverting input (+) exceeds the inverting input (−), the output goes high-impedance (pull-up resistor pulls it high). When inverting is higher, the output sinks to ground.

The LM393 uses a differential input stage similar to the LM358, but the output stage is completely different - a single NPN transistor with open collector instead of a class-AB linear output:

• You must add an external pull-up resistor
• The output can be pulled up to a different voltage than VCC (level shifting)
• Multiple outputs can be wired together (wired-OR)

The key spec is response time: 1.3 μs. From threshold crossing to output valid in about a microsecond. That's fast enough for voltage monitoring, zero-crossing up to ~50 kHz, and PWM applications.

Position in the product line: The LM393 is the general-purpose comparator. One step up is the LM393B (lower offset, faster, lower power). For higher speed, the TLV3501 (4.5 ns) or LM311 (200 ns). For lower power, the TLV1702 (55 μA/ch). The LM393's advantage is decades of production history and universal availability.

What Are the Specifications of LM393DR?

Key Parameter Commentary

• Response Time = 1.3 μs: Handles about 50 kHz square wave before delay matters. For higher frequencies, use LM311 (200 ns) or TLV3501 (4.5 ns).
• Open-collector output: Pull up to a different voltage than VCC for built-in level shifting. Always needs a pull-up resistor (1–10 kΩ). Lower R = faster rise, higher power.
• Input offset = 5 mV max: At 2.5V threshold, that's 0.2% error. Acceptable for most monitoring. For precision, use LM393B (0.37 mV typ).
• Common-mode includes ground: Same as LM358. Compare signals down to 0V in single-supply operation.
• Differential input = ±36V: Tolerates large differential voltages without damage. Not true for many rail-to-rail comparators.

What Is LM393DR Used For?

1. Voltage Level Detection

Over/under-voltage monitoring for power supplies and battery management. Open-collector output triggers MCU interrupt directly.

Key parameter: 1.3 μs response catches supply transients in the 10–100 μs range.

2. Zero-Crossing Detectors

AC zero-crossing for phase control (triac, dimmer, motor speed). Feed AC through a divider, bias at half-supply.

Key parameter: 1.3 μs gives ~0.02° accuracy at 50 Hz.

3. Relaxation Oscillators

Square wave generator with one comparator, RC network, and positive feedback. 2V–36V supply covers broad range.

Key parameter: Supply current ~0.8 mA per channel.

4. Window Comparators

Battery charge monitoring with two comparators for upper/lower limits. Wired-OR outputs for single fault signal.

Key parameter: Two comparators in SOIC-8. Perfect for battery window detection.

5. Level Shifting

Open-collector output allows different supply and pull-up voltages. 5V to 3.3V clean level shifting with no extra parts.

Key parameter: Pull-up to any voltage up to 15V.

6. PWM Detection

Threshold detection for motor control and power conversion signals.

Key parameter: 1.3 μs handles ~50 kHz PWM before edge errors.

LM393DR vs LM393B vs LM2903 vs LM339

Pick LM393DR: Cheapest, 2–36V, commercial temp. Baseline dual comparator.

Pick LM393B: Drop-in upgrade. Lower offset, faster, lower power, wider temp. Better for new designs.

Pick LM2903: Automotive temp (−40 to +125°C), slightly narrower supply.

Pick LM339DR: Four comparators instead of two. Same specs, larger package.

Frequently Asked Questions About LM393DR

Q1: What is the difference between LM393 and LM358?

A: LM393 is a comparator (open-collector output, digital). LM358 is an op-amp (linear output). Same pinout but not interchangeable.

Q2: Does LM393DR need a pull-up resistor?

A: Yes. Open-collector output can only sink. Add a pull-up (1kΩ–10kΩ) to your logic supply for a high output. No pull-up = no signal.

Q3: Can LM393DR work as an op-amp?

A: No. The open-collector output can't produce a linear voltage - it's either on or off. For linear amplification, use the LM358.

Q4: What is the maximum frequency?

A: About 50–100 kHz square wave. Above that, use LM311 (200 ns) or TLV3501 (4.5 ns).

Q5: What is the supply voltage range?

A: 2V to 36V single, or ±1V to ±18V dual. Minimum recommended is 2V.

Q6: How do I add hysteresis?

A: Add a resistor from output to non-inverting input (positive feedback). Typical values give 10–50 mV hysteresis to prevent oscillation near the threshold.

Q7: Can LM393DR drive a relay or LED?

A: LED with current-limiting resistor: yes (up to 20 mA). Relay coil (50–100 mA): no, use a transistor driver.

Q8: What are the best upgrades?

A: Drop-in: LM393B (1 μs, 0.37 mV offset, 200 μA/ch). Higher speed: LM311. Lower power: TLV1702. Quad: LM339DR.

Pricing & Availability

Stock: TI LM393DR and cross-compatible variants (LM393P, LM2903DR) in stock. Lead time: 2–5 business days.